The study, carried out in Stockholm - a city with comparatively low exhaust emissions - showed that ozone and fumes affect the foetus more than if the mother were a smoker.
Previous studies carried out in more polluted global cities has previously shown that the risk for premature birth is heightened. The Umeå study now reveals that even ground-level ozone poses a danger to pregnancy, according to a report in the Svenska Dagbladet (SvD) daily.
David Olsson, a PhD student in Public Health and Clinical Medicine and part of the research group, has expressed surprise at the results which show that the effect of air pollution is comparable to that of smoking during pregnancy.
"If we add up the effects of being exposed to high exhaust levels and ozone it has an even greater effect than smoking," he told SvD.
Ground-level ozone can disrupt the development of the placenta and thus influence the time of birth. In the later stages of pregnancy, traffic exhaust fumes have been found to cause the inflammation of mother's airways and expedite delivery.
Further studies have shown that premature babies carry a heightened risk of asthma and other respiratory problems.
According to Magnus Wickman, professor and chief physician at the Sachsska Children's Hospital in Stockholm, prescriptions for asthma medicines are more common among premature babies than those going to full term.